Method for producing hexafluoro-1,3-butadiene

Abstract

Provided is a method for producing hexafluoro-1,3-butadiene, the method being capable of producing hexafluoro-1,3-butadiene at high yields. The method for producing hexafluoro-1,3-butadiene comprises a reaction step of performing a dechlorination reaction, in which chlorine atoms are eliminated from 1,2,3,4-tetrachlorohexafluorobutane to produce hexafluoro-1,3-butadiene, in a reaction solution containing 1,2,3,4-tetrachlorohexafluorobutane, zinc, at least one of an antioxidant or a polymerization inhibitor, and an organic solvent.

Description

[Technical Field]

[0001] This invention relates to a method for producing hexafluoro-1,3-butadiene. [Background technology]

[0002] Hexafluoro-1,3-butadiene is useful, for example, as an etching gas for microfabrication of semiconductors. Various methods for producing hexafluoro-1,3-butadiene have been conventionally known. For example, Patent Document 1 discloses a method of dechlorinating 1,2,3,4-tetrachlorohexafluorobutane in 2-propanol in the presence of zinc. Patent Document 2 discloses a method of dehalogenating 1,4-diiodoperfluorobutane in tetrahydrofuran in the presence of magnesium. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 5005681 [Patent Document 2] Japanese Patent Publication No. 4684401 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, in the methods disclosed in Patent Documents 1 and 2, peroxides were sometimes produced as a by-product during the reaction, and side reactions mediated by radicals caused by these peroxides occurred. As a result of these side reactions, impurities and polymers were generated, which could lead to a decrease in the yield of hexafluoro-1,3-butadiene. The object of this invention is to provide a method for producing hexafluoro-1,3-butadiene in high yield. [Means for solving the problem]

[0005] To solve the aforementioned problems, one aspect of the present invention is as follows [1] to [8]. [1] A method for producing hexafluoro-1,3-butadiene, comprising a reaction step of carrying out a dechlorination reaction in a reaction solution containing 1,2,3,4-tetrachlorohexafluorobutane, zinc, at least one of an antioxidant and a polymerization inhibitor, and an organic solvent, to remove a chlorine atom from the 1,2,3,4-tetrachlorohexafluorobutane to produce hexafluoro-1,3-butadiene.

[0006] [2] The method for producing hexafluoro-1,3-butadiene according to [1], wherein the antioxidant is at least one of a radical chain initiation inhibitor, a radical scavenger, and a peroxide decomposer. [3] A method for producing hexafluoro-1,3-butadiene according to [1], wherein the antioxidant is a peroxide decomposer.

[0007] [4] A method for producing hexafluoro-1,3-butadiene according to [2] or [3], wherein the peroxide decomposing agent is 10H-phenothiazine. [5] A method for producing hexafluoro-1,3-butadiene according to any one of [1] to [4], wherein the polymerization inhibitor is a compound having a cyclohexadiene ring structure.

[0008] [6] A method for producing hexafluoro-1,3-butadiene according to any one of [1] to [5], wherein the ratio of the total molar amount of the antioxidant and the polymerization inhibitor to the molar amount of 1,2,3,4-tetrachlorohexafluorobutane is 0.01% or more and 10% or less.

[0009] [7] A method for producing hexafluoro-1,3-butadiene according to any one of the items [1] to [6], wherein the organic solvent is an alcohol. [8] The method for producing hexafluoro-1,3-butadiene according to [7], wherein the alcohol is at least one of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol. [Effects of the Invention]

[0010] According to the present invention, it is possible to produce hexafluoro-1,3-butadiene in a high yield.

Brief Description of the Drawings

[0011] [Figure 1] It is a diagram for explaining a reaction pathway in one embodiment of a method for producing hexafluoro-1,3-butadiene according to the present invention. [Figure 2] It is a schematic diagram for explaining the configuration of an apparatus for producing hexafluoro-1,3-butadiene used in Examples and Comparative Examples.

Modes for Carrying Out the Invention

[0012] One embodiment of the present invention will be described below. Note that this embodiment shows an example of the present invention, and the present invention is not limited to this embodiment. Also, various changes or improvements can be made to this embodiment, and forms with such changes or improvements can also be included in the present invention.

[0013] Conventional methods for producing hexafluoro-1,3-butadiene involve a reaction in a reaction solution containing 1,2,3,4-tetrachlorohexafluorobutane, zinc, and an organic solvent, in which all chlorine atoms are eliminated from 1,2,3,4-tetrachlorohexafluorobutane to produce hexafluoro-1,3-butadiene.

[0014] In the conventional method for producing hexafluoro-1,3-butadiene described above, the factors contributing to the decrease in yield of hexafluoro-1,3-butadiene are not fully understood. However, the inventors have found that side reactions occur due to peroxides produced as by-products during the reaction, and that these side reactions generate impurities and polymers, which is one of the factors contributing to the decrease in yield. The reaction pathway for producing hexafluoro-1,3-butadiene (C4F6) using 1,2,3,4-tetrachlorohexafluorobutane (C4Cl4F6) as a raw material will be explained with reference to Figure 1.

[0015] When 1,2,3,4-tetrachlorohexafluorobutane is dechlorinated in an organic solvent in the presence of zinc (Zn), the first step of dechlorination produces 3,4-dichloro-1,1,2,3,4,4-hexafluoro-1-butene (C4Cl2F6), a precursor of hexafluoro-1,3-butadiene. Then, the dechlorination of this 3,4-dichloro-1,1,2,3,4,4-hexafluoro-1-butene (the second step of dechlorination) produces hexafluoro-1,3-butadiene. Hereafter, 3,4-dichloro-1,1,2,3,4,4-hexafluoro-1-butene may be referred to as the "3,4-dichloro compound".

[0016] The reason why fluorocarbon impurities and polymers are produced as by-products in the dechlorination reaction described above is not clear, but as shown in Figure 1, it is presumed that fluorocarbon impurities and polymers are generated by side reactions between the precursor 3,4-dichloro compound and the target product hexafluoro-1,3-butadiene.

[0017] Therefore, after diligent research by the present inventors, it was found that by carrying out the above dechlorination reaction in the presence of at least one of an antioxidant and a polymerization inhibitor, the formation of fluorocarbon impurities and polymer by-products is suppressed, and the yield of hexafluoro-1,3-butadiene is improved. The reason why the formation of fluorocarbon impurities and polymer by-products is suppressed by the presence of antioxidants and polymerization inhibitors is not clear, but it is presumed that the peroxides formed as by-products during the reaction are reduced by the antioxidants and polymerization inhibitors, thereby suppressing side reactions mediated by radicals caused by the peroxides, and thus the formation of fluorocarbon impurities and polymer by-products is suppressed, and the yield of hexafluoro-1,3-butadiene is improved.

[0018] In other words, the method for producing hexafluoro-1,3-butadiene according to this embodiment comprises a reaction step in which a dechlorination reaction is carried out in a reaction solution containing 1,2,3,4-tetrachlorohexafluorobutane, zinc, at least one of an antioxidant and a polymerization inhibitor, and an organic solvent, to remove chlorine atoms from 1,2,3,4-tetrachlorohexafluorobutane to produce hexafluoro-1,3-butadiene.

[0019] According to the method for producing hexafluoro-1,3-butadiene of this embodiment, the formation of fluorocarbon impurities and polymer by-products is suppressed by at least one of the antioxidant and polymerization inhibitor, making it possible to produce hexafluoro-1,3-butadiene in high yield (for example, a yield of 85% or more).

[0020] The amount of hexafluoro-1,3-butadiene, the main product, and the amount of fluorocarbon impurities, a by-product, can be measured by gas chromatography. Furthermore, the amount of polymer produced can be estimated by subtracting the quantified amounts of hexafluoro-1,3-butadiene and fluorocarbon impurities from the amount of 1,2,3,4-tetrachlorohexafluorobutane used.

[0021] Here, we will explain fluorocarbon impurities and polymers. Fluorocarbon impurities include those with the chemical formula C4H x Cly F z Examples of compounds represented by (x, y, and z are positive integers) include pentafluoro-1,3-butadiene (C4HF5), chloropentafluoro-1,3-butadiene (C4ClF5), tetrafluoro-1,3-butadiene (C4H2F4), and dichlorohexafluorobutene (C4Cl2F6 (excluding its precursor, 3,4-dichloro compound)). These fluorocarbon impurities possess carbon-carbon double bonds and are therefore polymerizable.

[0022] Furthermore, as a fluorocarbon impurity, the chemical formula is C4H a O b Cl c F d Compounds represented by (a, b, c, and d are positive integers) are also included. For example, C4OF6, C4OCl2F6, and their dimers, trimers, and other polymers are included. Furthermore, examples of polymers include polymers of hexafluoro-1,3-butadiene, polymers of its precursor 3,4-dichloro compound, copolymers of hexafluoro-1,3-butadiene and its precursor 3,4-dichloro compound, and polymers of fluorocarbon impurities (see Figure 1).

[0023] In this invention, "hexafluoro-1,3-butadiene" means "1,1,2,3,4,4-hexafluoro-1,3-butadiene," and "1,2,3,4-tetrachlorohexafluorobutane" means "1,2,3,4-tetrachloro-1,1,2,3,4,4-hexafluorobutane."

[0024] The method for producing hexafluoro-1,3-butadiene according to this embodiment will be described in more detail below. [Antioxidants and polymerization inhibitors] The type of antioxidant is not particularly limited as long as it is difficult to inhibit the dechlorination reaction (hereinafter sometimes simply referred to as "dechlorination reaction") that eliminates chlorine atoms from 1,2,3,4-tetrachlorohexafluorobutane to generate hexafluoro-1,3-butadiene, has poor reactivity with zinc, and has solubility in an organic solvent. Examples include radical chain initiation inhibitors, radical scavengers, and peroxide decomposers.

[0025] Radical chain initiation inhibitors are classified into hydrazide-based antioxidants, amide-based antioxidants, etc. Specific examples of radical chain initiation inhibitors include N-salicyloyl-N'-aldehyde hydrazine, N-salicyloyl-N'-acetyl hydrazine, N,N'-diphenyl oxamide, and N,N'-di(2-hydroxyphenyl) oxamide.

[0026] Radical scavengers are classified into phenol-based antioxidants, amine-based antioxidants, etc. Specific examples of radical scavengers include 3,5-di-tert-butyl-4-hydroxytoluene (C 15 H 24 O), 2,2'-methylenebis(4-methyl-6-tert-butylphenol) (C 23 H 32 NO2), 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl free radical (C9H 18 NO2), N,N'-di-2-naphthyl-1,4-phenylenediamine (C 26 H 20 N2).

[0027] Peroxide decomposers are classified into sulfur-based antioxidants, phosphorus-based antioxidants, etc. Specific examples of peroxide decomposers include 10H-phenothiazine (C 12 H9NS), methyl-10H-phenothiazine (C 13 H 11 NS), chloro-10H-phenothiazine (C 12 H8ClNS), fluoro-10H-phenothiazine (C 12H8FNS), 2-mercaptobenzimidazole (C7H6N2S), terpene sulfide, triisodecyl phosphite (C 30 H 63 O3P), triphenyl phosphite (C 18 H 15 O3P is one example.

[0028] The type of polymerization inhibitor is not particularly limited, but compounds having a cyclohexadiene ring structure can be used. Specific examples of compounds having a cyclohexadiene ring structure include α-terpinene(4-methyl-1-(1-methylethyl)-1,3-cyclohexadiene(C) 10 H 16 )), γ-terpinene (4-methyl-1-(1-methylethyl)-1,4-cyclohexadiene (C 10 H 16 )), α-terpinolene (1-methyl-4-isopropylidene-1-cyclohexene (C 10 H 16 )), and others. These antioxidants and polymerization inhibitors may be used individually or in combination of two or more.

[0029] Among these antioxidants and polymerization inhibitors, 10H-phenothiazine is the most preferred because it is highly effective in improving the yield of hexafluoro-1,3-butadiene. The boiling point of 10H-phenothiazine is 371°C, and the boiling point of hexafluoro-1,3-butadiene is 5.4°C. Therefore, if the reaction temperature for the dechlorination reaction is, for example, 50-100°C, the vapor produced when the reaction solution vaporizes will mainly contain hexafluoro-1,3-butadiene and organic solvents, and the amount of 10H-phenothiazine mixed into the vapor is considered to be trace.

[0030] Even if 10H-phenothiazine is present in the vapor generated when the reaction solution vaporizes, it can be easily separated from the vapor through purification processes such as distillation or adsorption. Therefore, it is possible to use 10H-phenothiazine in the production process of hexafluoro-1,3-butadiene.

[0031] While a higher total amount of antioxidants and polymerization inhibitors used (a higher total concentration of antioxidants and polymerization inhibitors in the reaction solution) tends to improve the yield of hexafluoro-1,3-butadiene, the ratio of the total molar amount of antioxidants and polymerization inhibitors to the molar amount of 1,2,3,4-tetrachlorohexafluorobutane is preferably 0.01% to 10%, more preferably 0.05% to 5%, and even more preferably 0.1% to 2%.

[0032] The antioxidant and polymerization inhibitor may be dissolved in at least one of an organic solvent and 1,2,3,4-tetrachlorohexafluorobutane, and the solution may be supplied to a reaction vessel such as an autoclave for the dechlorination reaction, or it may be supplied to the reaction vessel as is for the dechlorination reaction.

[0033] Furthermore, when supplying antioxidants and polymerization inhibitors directly to batch reaction vessels, the order in which the antioxidants, polymerization inhibitors, zinc, and organic solvents are supplied to the reaction vessels is not particularly limited and can be supplied in any order. For example, the antioxidants and polymerization inhibitors may be added to the reaction vessel containing zinc and organic solvents, or the zinc and organic solvents may be added to the reaction vessel containing antioxidants and polymerization inhibitors. However, when the reaction process is carried out in a continuous reactor, it is necessary to add the antioxidants, polymerization inhibitors, zinc, and organic solvents to the reactor simultaneously.

[0034] 〔zinc〕 The form of zinc is not particularly limited as long as it allows the dechlorination reaction to proceed, but from the viewpoint of reactivity and ease of handling, a powder form is preferred. The average particle size of the powdered zinc is preferably 0.04 mm to 1.0 mm, more preferably 0.04 mm to 0.50 mm, and even more preferably 0.04 mm to 0.10 mm.

[0035] The amount of zinc used is not particularly limited as long as the dechlorination reaction proceeds, but the ratio of the molar amount of zinc to the molar amount of 1,2,3,4-tetrachlorohexafluorobutane (zinc / 1,2,3,4-tetrachlorohexafluorobutane) is preferably 0.1 to 10, more preferably 1.0 to 5.0, and even more preferably 2.0 to 3.0.

[0036] [Organic solvents] The type of organic solvent is not particularly limited as long as it does not inhibit the dechlorination reaction. Furthermore, the organic solvent is preferable if it readily dissolves the antioxidant, has poor reactivity with zinc, has good zinc dispersibility, and the solubility of the by-product zinc chloride (ZnCl2) is not zero.

[0037] Suitable organic solvents include, for example, alcohols, cyclic ethers, acetone (C2H6CO), acetonitrile (CH3CN), aromatic hydrocarbons, amide solvents, organic acids, N-methyl-2-pyrrolidone (C5H9NO), or mixtures thereof. Among these organic solvents, alcohols are preferred because they allow the dechlorination reaction to proceed smoothly.

[0038] Specific examples of alcohols include methanol (CH3OH), ethanol (C2H5OH), 1-propanol (C3H7OH), 2-propanol (C3H7OH), 1-butanol (C4H9OH), and 2-butanol (C4H9OH). Of these, 2-propanol is the most suitable in terms of ease of handling.

[0039] Examples of cyclic ethers include tetrahydrofuran (C4H8O) and 1,4-dioxane (C4H8O2). Examples of aromatic hydrocarbons include benzene (C6H6) and toluene (C7H8). Examples of amide solvents include N,N-dimethylformamide (C3H7NO). Examples of organic acids include acetic acid (CH3COOH). One organic solvent may be used alone, or two or more may be used in combination.

[0040] The amount of organic solvent used is not particularly limited as long as the dechlorination reaction proceeds, but the ratio of the molar amount of organic solvent to the molar amount of 1,2,3,4-tetrachlorohexafluorobutane (organic solvent / 1,2,3,4-tetrachlorohexafluorobutane) is preferably 0.1 or more and 10 or less, more preferably 1.0 or more and 9.0 or less, and even more preferably 3.0 or more and 8.0 or less.

[0041] [Reaction conditions] The reaction temperature for the dechlorination reaction is not particularly limited as long as the dechlorination reaction proceeds, but it is preferably 20°C to 150°C, more preferably 40°C to 130°C, and even more preferably 70°C to 100°C.

[0042] The reaction pressure for the dechlorination reaction is not particularly limited as long as the dechlorination reaction proceeds, but it is preferably 0.01 MPa or more and 1 MPa or less in absolute pressure, more preferably 0.05 MPa or more and 0.5 MPa or less in absolute pressure, and even more preferably 0.08 MPa or more and 0.2 MPa or less in absolute pressure. [Examples]

[0043] The present invention will be described in more detail below with reference to examples and comparative examples. [Example 1] The reaction was carried out using the hexafluoro-1,3-butadiene production apparatus shown in Figure 2. 471 g (7.84 mol) of 2-propanol as an organic solvent and 0.39 g (0.0020 mol) of 10H-phenothiazine (labeled "PTZ" in Table 1) as an antioxidant were added to a 1 L SUS316 autoclave 1, and the 10H-phenothiazine was dissolved in the 2-propanol. Then, 327 g (5.00 mol, average particle size 0.075 mm. The particle size distribution was measured using a Microtrac MT3300 laser diffraction analyzer manufactured by Microtrac Bell Co., Ltd. The average particle size was calculated from the area average value. The number of measurements n was 3.) was added. The ratio of the amount of 10H-phenothiazine used (moles) to the amount of 1,2,3,4-tetrachlorohexafluorobutane used (moles) was 0.1%. This autoclave 1 is equipped with a jacket (not shown) and a stirrer (not shown) on top, and the heating method is a jacket heating method.

[0044] The contents of autoclave 1 were stirred while the temperature was raised to 80°C. A Dieblot condenser 3 was attached to the outlet of autoclave 1. Then, while maintaining the temperature of the contents of autoclave 1 at 80°C under atmospheric pressure, 608 g (2.00 mol) of 1,2,3,4-tetrachlorohexafluorobutane was added dropwise from the 1,2,3,4-tetrachlorohexafluorobutane supply device 2 at a rate of 2.0 g per minute to carry out the reaction.

[0045] After approximately 5 hours of dropwise dispensing, the temperature of the contents was raised to 95°C, and a portion of the 2-propanol and the product were vaporized at atmospheric pressure over 2 hours. These vapors were then sent to a trap (first trap 4A) cooled to -78°C to cool and liquefy, and 263.2 g of the first fraction was collected. Analysis of this first fraction by gas chromatography revealed that it was crude hexafluoro-1,3-butadiene with a hexafluoro-1,3-butadiene content of 95.3% by mass.

[0046] Next, the temperature of the contents of autoclave 1 was returned to room temperature, and the operation of the Dieblot condenser 3 was stopped. Then, nitrogen gas (N2) was flowed through autoclave 1 at a flow rate of 100 mL / min to vaporize the product remaining in autoclave 1. The vapor was then sent to a trap (second trap 4B) cooled to -78°C to cool and liquefy, and 8.0 g of the second fraction was collected. Analysis of this second fraction by gas chromatography revealed that it was crude hexafluoro-1,3-butadiene with a hexafluoro-1,3-butadiene content of 84.1% by mass. The total yield of hexafluoro-1,3-butadiene (indicated as "C4F6 in the fraction" in Table 1) from the first and second fractions was 82.8%. In addition, the components that did not vaporize and remained in autoclave 1 (including solvent, polymers, and by-product impurities) were subjected to analysis as residue.

[0047] Here, the definition of the yield of C4F6 is as follows: C4F6 yield (%) = {[Mass of first fraction] × [Percentage of hexafluoro-1,3-butadiene in the first fraction] / [Molecular weight of C4F6 (162.03)] + [Mass of second fraction] × [Percentage of hexafluoro-1,3-butadiene in the second fraction] / [Molecular weight of C4F6 (162.03)]} / [Moles of 1,2,3,4-tetrachlorohexafluorobutane charged] × 100

[0048] The residue remaining in autoclave 1 after collecting the first and second fractions was analyzed by gas chromatography. From the analysis of the first fraction, second fraction, and residue, it was found that in the reaction of Example 1, C4Cl2F6 (excluding the precursor), fluorocarbon impurities other than C4Cl2F6, and polymers were produced as by-products.

[0049] Furthermore, the ratio of moles of by-product C4Cl2F6 (excluding precursors) to moles of 1,2,3,4-tetrachlorohexafluorobutane charged (yield) was 1.8%, the ratio of moles of fluorocarbon impurities other than C4Cl2F6 (labeled "Other" in Table 1) to moles of 1,2,3,4-tetrachlorohexafluorobutane charged (yield) was 6.7%, and the ratio of moles of by-product polymers to moles of 1,2,3,4-tetrachlorohexafluorobutane charged (yield) was 6.6%. In addition, the ratio of moles of C4F6 remaining in the residue to moles of 1,2,3,4-tetrachlorohexafluorobutane charged was 1.9% (the yield of C4F6 in the residue was 1.9%).

[0050] The conversion rate of the 1,2,3,4-tetrachlorohexafluorobutane used was 100%, and all products except C4F6, C4Cl2F6 (excluding the precursor), and fluorocarbon impurities were considered polymers. The number of moles of by-product polymers was calculated using a simplified method, rather than the number of moles converted from the molecular weight of the polymers. This method involved subtracting the total number of moles of C4F6, C4Cl2F6 (excluding the precursor), and fluorocarbon impurities from the number of moles of the 1,2,3,4-tetrachlorohexafluorobutane used. The results are summarized in Table 1.

[0051] [Table 1]

[0052] The measurement conditions for gas chromatography of the first and second fractions are as follows: Measurement device: Gas chromatograph GC-2014 manufactured by Shimadzu Corporation Column: Agilent Technologies, Inc. CP-PoraPLOT Q-HT gas chromatograph column Column heating conditions: 90°C (0 min) → (5°C / min) → 230°C (5 min) Column equilibrium time: 1 min Initial temperature at the pouring port: 120℃ Control mode: Pressure Pressure: 46.5 kPa (constant) Total flow rate: 54.0mL / min Column flow rate: 1.0 mL / min Linear speed: 23.1cm / sec Split ratio: 50 Carrier gas: He Detector: Flame ionization detector (FID) Detector temperature: 230℃ Hydrogen pressure: 60kPa Air pressure: 50kPa Sample injection volume: 0.2 mL (gas)

[0053] The measurement conditions for gas chromatography of the residue are as follows: Measurement device: Gas chromatograph GC-2014 manufactured by Shimadzu Corporation Column: DB-1 gas chromatograph column manufactured by Agilent Technologies, Inc. Column heating conditions: 40°C (15 min) → (10°C / min) → 230°C (31 min) Column equilibrium time: 2 min Initial temperature at the pouring port: 200℃ Control mode: Pressure Pressure: 100kPa (constant) Total flow rate: 24.1mL / min Column flow rate: 1.75 mL / min Linear speed: 25cm / sec Purge flow rate: 3 mL / min Split ratio: 11 Carrier gas: He Detector: Flame ionization detector (FID) Detector temperature: 230℃ Hydrogen pressure: 60kPa Air pressure: 50kPa Sample injection volume: 0.2 mL (liquid)

[0054] [Example 2] The dechlorination reaction was carried out in the same manner as in Example 1, except that the amount of 10H-phenothiazine used was 3.9 g (0.020 mol). The ratio of the amount of 10H-phenothiazine used (moles) to the amount of 1,2,3,4-tetrachlorohexafluorobutane used (moles) was 1.0%. As a result, a first fraction of 283.0 g, a second fraction of 7.8 g, and a residue were obtained.

[0055] Analysis of the first fraction, second fraction, and residue by gas chromatography revealed that the hexafluoro-1,3-butadiene content in the first fraction was 95.4% by mass, and the hexafluoro-1,3-butadiene content in the second fraction was 86.3% by mass. The total yield of hexafluoro-1,3-butadiene from the first and second fractions combined was 85.0%. The results of the analysis, performed in the same manner as in Example 1, are summarized in Table 1.

[0056] [Example 3] The dechlorination reaction was carried out in the same manner as in Example 1, except that 4.4 g (0.020 mol) of 3,5-di-tert-butyl-4-hydroxytoluene (referred to as "BHT" in Table 1) was used as an antioxidant instead of 10H-phenothiazine. The ratio of the amount of 3,5-di-tert-butyl-4-hydroxytoluene used (moles) to the amount of 1,2,3,4-tetrachlorohexafluorobutane used (moles) was 1.0%. As a result, 223.9 g of the first fraction, 32.0 g of the second fraction, and a residue were obtained.

[0057] Analysis of the first fraction, second fraction, and residue by gas chromatography revealed that the hexafluoro-1,3-butadiene content in the first fraction was 94.5% by mass, and the hexafluoro-1,3-butadiene content in the second fraction was 85.3% by mass. The total yield of hexafluoro-1,3-butadiene from the first and second fractions combined was 73.5%. The results of the analysis, performed in the same manner as in Example 1, are summarized in Table 1.

[0058] [Example 4] The dechlorination reaction was carried out in the same manner as in Example 1, except that 2.7 g (0.020 mol) of α-terpinene, a polymerization inhibitor, was used instead of an antioxidant. The ratio of the amount of α-terpinene used (moles) to the amount of 1,2,3,4-tetrachlorohexafluorobutane used (moles) was 1.0%. As a result, 208.3 g of the first fraction, 46.8 g of the second fraction, and a residue were obtained.

[0059] Analysis of the first fraction, second fraction, and residue by gas chromatography revealed that the hexafluoro-1,3-butadiene content in the first fraction was 95.1% by mass, and the hexafluoro-1,3-butadiene content in the second fraction was 88.6% by mass. The total yield of hexafluoro-1,3-butadiene from the first and second fractions combined was 73.7%. The results of the analysis conducted in the same manner as in Example 1 are summarized in Table 1.

[0060] [Example 5] The dechlorination reaction was carried out in the same manner as in Example 1, except that 3.4 g (0.020 mol) of 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl free radical (labeled "4H-TEMPO" in Table 1) was used as an antioxidant instead of 10H-phenothiazine. The ratio of the amount of 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl free radical used (molar amount) to the amount of 1,2,3,4-tetrachlorohexafluorobutane used (molar amount) was 1.0%. As a result, 215.0 g of the first fraction, 40.5 g of the second fraction, and the residue were obtained.

[0061] Analysis of the first fraction, second fraction, and residue by gas chromatography revealed that the hexafluoro-1,3-butadiene content in the first fraction was 94.8% by mass, and the hexafluoro-1,3-butadiene content in the second fraction was 88.6% by mass. The total yield of hexafluoro-1,3-butadiene from the first and second fractions combined was 73.9%. The results of the analysis, performed in the same manner as in Example 1, are summarized in Table 1.

[0062] [Comparative Example 1] The dechlorination reaction was carried out in the same manner as in Example 1, except that antioxidants and polymerization inhibitors were not used. As a result, 207.0 g of the first fraction, 42.7 g of the second fraction, and a residue were obtained. Analysis of the first fraction, second fraction, and residue by gas chromatography revealed that the hexafluoro-1,3-butadiene content in the first fraction was 94.6% by mass, and the hexafluoro-1,3-butadiene content in the second fraction was 87.2% by mass. The total yield of hexafluoro-1,3-butadiene from the first and second fractions combined was 71.7%. The results of the analysis, performed in the same manner as in Example 1, are summarized in Table 1. [Explanation of Symbols]

[0063] 1. Autoclave 2...Feeding device 3. Dimroth condenser 4A...First Trap 4B...Second Trap

Claims

1. A method for producing hexafluoro-1,3-butadiene, comprising a reaction step of carrying out a dechlorination reaction in which a chlorine atom is removed from 1,2,3,4-tetrachlorohexafluorobutane to produce hexafluoro-1,3-butadiene in a reaction solution containing 1,2,3,4-tetrachlorohexafluorobutane, zinc, an antioxidant, and an organic solvent.

2. The method for producing hexafluoro-1,3-butadiene according to claim 1, wherein the antioxidant is at least one of a radical chain initiation inhibitor, a radical scavenger, and a peroxide decomposer.

3. A method for producing hexafluoro-1,3-butadiene according to claim 1, wherein the antioxidant is a peroxide decomposer.

4. A method for producing hexafluoro-1,3-butadiene according to any one of claims 1 to 3, wherein the ratio of the molar amount of the antioxidant to the molar amount of 1,2,3,4-tetrachlorohexafluorobutane is 0.01% or more and 10% or less.

5. A method for producing hexafluoro-1,3-butadiene according to any one of claims 1 to 3, wherein the organic solvent is an alcohol.

6. The method for producing hexafluoro-1,3-butadiene according to claim 5, wherein the alcohol is at least one of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol.

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